Protectant for UV-Induced Skin Damage

ABSTRACT

The present invention provides a method for protecting against UV radiation-induced skin damage. Specifically, compositions including dapsone are administered to provide UV protection. The dapsone compositions may be administered orally, or by other parenteral routes, such as topically, transdermally, by inhalation, and the like.

FIELD OF THE INVENTION

The present invention relates to the field of dermatologic pharmacology.In particular, UV protectants that reduce the risk of skin damage aredescribed. The compositions are formulated with dapsone as the activeprotective ingredient.

BACKGROUND OF THE INVENTION

Human skin is a primary target of nonionizing electromagnetic radiationin the ultraviolet, visible, and infrared ranges, and consists of threedistinct layers: the stratum corneum, the epidermis, and the dermis. Theepidermis and dermis contain several molecules known as chromophores,that are capable of absorbing light or UV radiation (UVR). The mainchromophores in human skin include such molecules as nucleic acids,aromatic amino acids, proteins, porphyrins, carotenoids, steroids, andquinones (Mary S. Matsui and Vincent A. DeLeo, Skin Cancer: Mechanismsand Human Relevance Chp. 4, 22 (Hasan Mukhtar ed., 1995)).

The UV spectrum is divided into A, B, and C ranges. The UVC rangeextends from wavelengths between 200 and 290 nm. The UVB spectrumincludes wavelengths between 290 and 320 nm, and is generally known asthe sunburn spectrum because it produces erythema in human skin. UVAradiation includes wavelengths between 320 to 400 nm. Atmospheric ozoneabsorbs all UVC and much of the UVB, so that the spectrum of UVradiation at the earth's surface consists primarily of UVA. The depth towhich a photon penetrates in vivo is related to its wavelength. Thus,most UVB radiation transmitted through the ozone layer is absorbedwithin the first 0.03 mm of the epidermis, whereas one third of UVAradiation penetrates to a depth of 0.1 mm (Hardie et al., Surgery 87:177(1980)).

When the skin is exposed to UVR, energy transferred to chromophores fromthe absorbed radiation may result in molecular reorganization and/orinteraction with nearby biomolecules. For example, after UVR absorption,DNA may form dipyrimidine lesions, such as cyclobutane pyrimidinedimers. In turn, characteristic mutations result, e.g., mutations inp53, that have been shown to be important in producing non-melanoma skincancer. (A. Ziegler et al., Nature 372:773-776 (1994)). Furthermore, theUV-induced conversion of urocanic acid from the trans to cis isomer hasbeen linked to the subsequent development of non-melanoma skin cancers(Craig A. Elmets et al., Skin Cancer: Mechanisms and Human RelevanceChp. 18, 230 (Hasan Mukhtar ed., 1995)).

Further insight into UV-induced skin tumor formation has been gainedfrom studies in rodents. UV-induced skin tumors stimulate a strongimmune response. If UV-induced tumors are implanted into normal,genetically identical mice, they are promptly rejected by the hostimmune-system and the animals survive. If the same tumor is implantedinto mice that have been exposed to subcarcinogenic doses of UVR,immunological destruction of the tumor does not occur. These resultsindicate that UVR produces mutations in skin cells and facilitates tumorgrowth by impairing immune surveillance. The presence of bothdeficiencies is necessary for clinically apparent skin cancers todevelop (J. T. Krutmann and C. A. Elmets eds. (1995). Photoimmunology.Oxford: Blackwell Scientific).

Currently marketed sunscreens function either as ultraviolet (UV)filters or UV blocks. UV blocks, such as TiO₂ and ZnO, as well asderivatives of other metal-oxides, form a physical barrier that scattersUV light. These UV blocks offer the most comprehensive sunscreenprotection, blocking the full spectrum of UVA and UVB light. However,the most commonly used sunscreens are UV filters, which are typicallyorganic compounds. A disadvantage of UV filters is that each organiccompound has a limited range of maximum UV absorptivity, rendering eachreagent better suited for either UVA protection or UVB protection, butnot both.

The UV-induced mouse tumor model has proven very useful not only ingaining mechanistic understanding of skin tumor formation, but also indetermining if topical products promote or inhibit the formation ofUV-induced tumors. A standard UV carcinogenicity model accepted for thetesting of topical pharmaceuticals employs the albino hairlessCrl:SKH1-hr BR mouse (P. D. Forbes et al., Photobiology. 663-669 (E.Riklis ed., 1991)).

After administration of a topical formulation, experimental protocolstypically instruct that mice be irradiated once daily, five days perweek, for 40 weeks. Intensity and cumulative UV radiation dose ismeasured in Robertson-Bergen Units (RBU). The RBU is a measure ofbiological effectiveness for UVR, with 400 RBU being approximately oneminimal erythema dose in previously untanned human skin, i.e., about 30mJ/cm² in a sun-sensitive skin type I or II. Mouse carcinogenicitystudies are completed at 600 RBU per week because this produces anappropriate tumor mean latent period for comparison with test articletreated and untreated controls. At this radiation level, about half ofthe untreated animals will have a first perceptible tumor by weekforty-one. A higher control UVR level of 1200 RBU per week results in asignificant reduction in the median tumor latent period. At thisradiation dose, about half of the untreated animals will have a firstperceptible tumor by week twenty-four. Animals continue to be observedfor 12 weeks after 40 weeks of product application to provide a total of52 weeks of tumor data.

At least two common topical therapies promote tumor formation in this UVinduced mouse carcinogenicity model. Benzoyl peroxide and retinoids suchas tretinoin, which are commonly used to treat acne, promote theformation of skin tumors compared to untreated or vehicle controls.(Physicians Desk Reference, 56^(th) Edition, Medical Economics Company,Inc., Montvale N.J., (2002)). While many topical products containingthese actives are currently in use, the patients who use them arestrongly encouraged to avoid sun exposure on their face after using theproduct. However, significantly shielding the face from sun exposure,especially for young adults, is virtually impossible for products thatare often used twice daily.

U.S. Pat. No. 6,113,888 to Castro et al.; U.S. Pat. No. 6,200,964 toSingleton et al.; and U.S. Pat. No. 6,231,837 to Stroud et al. describetopical compositions that contain therapeutics. However, the therapeuticis not included to provide protection from ultraviolet radiation. If UVRprotection is desired, sunscreens are added to the formulations.

Topical compositions including dapsone have been described in U.S. Pat.Nos. 5,863,560 and 6,060,085 to Osborne, and U.S. application Ser. No.10/081,050 to Osborne, which are herein incorporated by reference intheir entirety. However, these compositions were formulated to treatacne, not to prevent skin damage from UV radiation.

Therefore, new compositions that protect against UV-induced skin damageare needed.

SUMMARY OF THE INVENTION

The present invention is a method for protecting against UVradiation-induced skin damage in individuals by selecting individuals inneed of protection from UV radiation and administering to them acomposition that includes dapsone. In general, selection of theindividual in need of protection from UV radiation is based upon factorssuch as the frequency and duration of UV radiation exposure, e.g., sunexposure, and/or the risk of the individual for UV-induced skin damage.In turn, the risk is typically assessed by examining such factors as theindividual's age and predisposition to sunburn or develop pigmentedlesions after sun exposure, any genetic predisposition to skin cancer,prior medical history of UV-induced skin damage, and presentation ofV-induced skin damage at the time of examination.

The dapsone compositions may be provided in formulations including, butnot limited to, gels, creams, lotions, solutions, hydrophilic orhydrophobic ointments, microemulsions, shake-powders, aerosol and pumpsprays, tablets, capsules, patches, films, and suppositories. Thedapsone used in the compositions may be in dissolved or particulateform, or a mixture of dissolved and microparticulate dapsone. Thecomposition that is administered may also include additives such aspreservatives, antioxidants, fragrances, or colorants.

Besides protecting against signs of aging (e.g., wrinkles) andhyperpigmentation, compositions including dapsone may be administered toprotect against the formation, in other words, prevent the developmentof, UV-induced premalignant skin lesions such as actinic keratosis, aswell as UV-induced malignant tumors of the skin. In another embodiment,the dapsone compositions may be administered to individuals having atleast one premalignant skin lesion to prevent the premalignant skinlesion from becoming a malignant skin tumor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a decrease in prevalence of tumor formation in albinohairless mice exposed to UVR at 600 and 1200 RBU with the use of varioustopical dapsone compositions.

DETAILED DESCRIPTION OF THE INVENTION

The inventive methods provide dapsone compositions that protect againstultraviolet radiation-induced skin damage.

As used herein, the terms “UV-induced skin damage” or “UV-induced skindisorder” do not refer to acne. These terms are used interchangeably andrefer to skin damage resulting from exposure to ultraviolet light in theA (320-400 nm), B (290-320 nm), or C ranges (200-290 nm). Examples ofUV-induced skin damage, also referred to herein as “skin lesions”,include wrinkles, hyperpigmentation, dysplasias such as actinickeratosis, and malignant skin tumors such as squamous cell or basal cellcarcinoma.

As used herein, the term “protects” or “protecting” refers to areduction in the amount of skin damage which can be manifested, e.g., bya decrease in the number and/or severity of individual skin lesions, orprevention of the development of skin lesions.

The term “topical” as used herein refers to the route of administrationof a composition that involves direct application to the body part beingtreated, e.g., the skin for dermatological compositions. Examples oftopical application include application to the skin of gels or othersemisolids to rub-on, solutions to spray, or liquids to be applied by anapplicator. Rinse-off application with washes, cleansers, or shampoosare also examples of topical application. Typically, areas of the bodysuitable for application of compositions having dapsone include the skinof the face, throat, neck, scalp, chest, back, ears, and other skinsites where sun exposure may occur.

By use of the term “dapsone” it is meant the chemical compound dapsonehaving the chemical formula C₁₂H₁₂N₂O₂S as well asbis(4-aminophenyl)sulfone, 4′,4′-diaminodiphenyl sulfone and itshydrates, 4,4′-sulfonylbisbenzeneamine, 4,4′-sulfonyldianiline,diaphenylsulfone, dapsone analogs, and dapsone related compounds.“Dapsone analogs” refers to chemical compounds that have similarchemical structures and thus similar therapeutic potential to dapsonesuch as the substituted bis(4-aminophenyl)-sulfones. “Dapsone relatedcompounds” refers to chemical compounds that have similar therapeuticactivity, but are not as closely related by chemical structure todapsone such as the substituted 2,4-diamino-5-benzylpyrimidines.

Dapsone Compositions Dapsone Topical Gel

The topical gel compositions of this invention utilize various forms ofdapsone. For instance, in one embodiment, dapsone may be present in thecomposition as only dissolved dapsone. In another embodiment, dapsonemay be present in the composition only as microparticulate dapsone. In afurther embodiment, the dermatological composition exhibits an optimalbalance between dissolved dapsone that is available to cross through thestratum corneum to become systemically available, and microparticulatedapsone that is retained in or above the stratum corneum to serve as areservoir or to provide dapsone to the supracorneum zone. Themicroparticulate dapsone may comprise a crystalline precipitant or anamorphous precipitant.

In one embodiment, the dermatological composition that is appliedcomprises a semi-solid or gel-like vehicle that may include a polymerthickener, water, preservatives, active surfactants or emulsifiers,antioxidants, sunscreens, and a solvent or mixed solvent system. Thesolvent or mixed solvent system is important to the formation of themicroparticulate to dissolved dapsone ratio. The formation of themicroparticulate, however, should not interfere with the ability of thepolymer thickener or preservative systems to perform their functions.

Polymer thickeners that may be used include those known to one skilledin the art, such as hydrophilic and hydroalcoholic gelling agentsfrequently used in the cosmetic and pharmaceutical industries.Preferably, the hydrophilic or hydroalcoholic gelling agent comprises“CARBOPOL®” (B.F. Goodrich, Cleveland, Ohio), “HYPAN®” (KingstonTechnologies, Dayton, N.J.), “NATROSOL®” (Aqualon, Wilmington, Del.),“KLUCEL®” (Aqualon, Wilmington, Del.), or “STABILEZE®” (ISPTechnologies, Wayne, N.J.). Preferably, the gelling agent comprisesbetween about 0.2% to about 4% by weight of the composition. Moreparticularly, the preferred compositional weight percent range for“CARBOPOL®” is between about 0.5% to about 2%, while the preferredweight percent range for “NATROSOL® and “KLUCEL®” is between about 0.5%to about 4%. The preferred compositional weight percent range for both“HYPAN®” and “STABILEZE®” is between about 0.5% to about 4%.

“CARBOPOL®” is one of numerous cross-linked acrylic acid polymers thatare given the general adopted name carbomer. These polymers dissolve inwater and form a clear or slightly hazy gel upon neutralization with abase such as sodium hydroxide, potassium hydroxide, triethanolamine, orother amine bases. “KLUCEL®” is a cellulose polymer that is dispersed inwater and forms a uniform gel upon complete hydration. Other preferredgelling polymers include hydroxyethylcellulose, hydroxypropylcellulose,cellulose gum, MVA/MA copolymers, MVE/MA decadiene crosspolymer, PVM/MAcopolymer, or a combination thereof.

Preservatives may also be used in this dermatological composition andpreferably comprise about 0.05% to 0.5% by weight of the totalcomposition. The use of preservatives assures that if the product ismicrobially contaminated, the formulation will prevent or diminishmicroorganism growth. Some preservatives useful in this inventioninclude methylparaben, propylparaben, butylparaben, chloroxylenol,sodium benzoate, DMDM Hydantoin, 3-Iodo-2-Propylbutyl carbamate,potassium sorbate, chlorhexidine digluconate, or a combination thereof.

In one embodiment, the dermatological composition that is appliedincludes 0.5% to 4.0% carbomer and about 0.5% to 10% dapsone that existsin both a dissolved state and a microparticulate state. In anotherembodiment, the dermatological composition comprises about 1% carbomer,about 80-90% water, about 10% (diethylene glycol monoethyl ether (DGME),about 0.2% methylparaben, and about 0.3% to 3.0% dapsone including bothmicroparticulate dapsone and dissolved dapsone, and about 2% of a base.More particularly, the carbomer may include “CARBOPOL® 980” and the basemay include sodium hydroxide solution.

In a another embodiment, the composition comprises dapsone andethoxydiglycol, which allows for an optimized ratio of microparticulatedrug to dissolved drug. This ratio determines the amount of drugdelivered, compared to the amount of drug retained in or above thestratum corneum to function in the supracorneum domain. The system ofdapsone and DGME may include purified water combined with “CARBOPOL®”gelling polymer, methylparaben, propylparaben, titanium dioxide, BHA,and a base to neutralize the “CARBOPOL®.”

Dapsone Topical Cream or Lotion

In another embodiment, dapsone may be applied as a topical cream orlotion in which dapsone may be dissolved or dispersed or both partiallydissolved and partially dispersed. Topical creams or lotions may beeither oil-in-water emulsions or water-in-oil emulsions. The oil phasemay include but is not limited to fatty alcohols, acids, or esters suchas cetyl palmitate, cetyl alcohol, stearyl alcohol, stearic acid,isopropyl stearate, glycerol stearate, mineral oil, white petrolatum, orother oils alone or in combination. The topical creams or lotions may beformulated for use as sunscreens.

Emulsifiers that may be added to the composition include, but are notlimited to, steareth 20, ceteth 20, sorbitan sesquioleate, sorbitanmono-oleate, propylene glycol stearate, dosium lauroyl sarcosinate,polysorbate 60, or combination. Preservatives, antioxidants, fragrances,colorants, thickeners, and other additives required to achieve apharmaceutically or cosmetically acceptable or preferred product mayalso be included. However, topical creams and lotions are not limited tothese components since one skilled in the art will be aware ofadditional components useful in the formulation of topical creams andlotions.

Dapsone Topical Solution or Suspension

In another embodiment, dapsone may be applied as a solution orsuspension. These are fluid solvent or mixed-solvent systems including,but not limited to, water, ethanol, propylene glycol, glycerol,polyethylene glycol, ethyl acetate, propylene carbonate,n-methylpyrrolidone, triethanolamine, 1,4-butanediol, triacetin,diacetin, dimethyl isosorbide alone or in combination. Preservatives,antioxidants, fragrances, colorants, thickeners, suspending agents,enhancers, and other additives required to achieve pharmaceutically orcosmetically acceptable or preferred product may also be included.Again, topical solutions or suspensions are not limited to thesecomponents, since one skilled in the art will be aware of additionalcomponents useful in the formulation of topical solutions orsuspensions.

Additional Dapsone Formulations

Dapsone may also be topically applied using a pharmaceutical or cosmeticcarrier form such as a hydrophobic or hydrophilic ointment, roll-on orstick product, microemulsion, shake powder, an aerosolized spray ormousse, a pump spray or mousse, or bath additive. Examples of ointmentsinclude essentially non-aqueous mixtures of petrolatum, lanolin,polyethylene glycol, plant or animal oils, either hydrogenated orotherwise chemically modified. An ointment may also contain a solvent inwhich dapsone is either fully or partially dissolved. Additionalpharmaceutical carriers will be known to those skilled in the art andthis list should not be considered to be limiting.

In addition to topical compositions, dapsone may be formulated aspharmaceutical preparations including, but not limited to, granules,tablets, suppositories, capsules, suspensions, patches, films, andaerosols. Pharmaceutical grade organic or inorganic carriers and/ordiluents suitable for inhalation or oral, parenteral, transmucosal, ortransdermal administration may be used to formulate compositionsincluding dapsone. Stabilizing agents, wetting and emulsifying agents,salts for varying the osmotic pressure, or buffers for securing anadequate pH value may also be included in the dapsone compositions.

Administration of Dapsone Compositions

In addition to topical administration, dapsone, dapsone analogs, ordapsone related compounds may have sufficient partitioning to the skinor sufficient activity in the skin to be delivered by other routes ofadministration. For example, systemic dosing may accompany topicaldosing, or systemic dosing for the purpose of photoprotection may beused as a singular therapy. Other routes and methods of administrationwill be known to those skilled in the art. These include, but are notlimited to, oral, rectal, vaginal, nasal, ocular, oral transmucosal andother transmucosal, transdermal, parenteral, and pulmonary routes.Parenteral administration includes, without limitation, intravenous,subcutaneous, intramuscular, intra-arterial, intrathecal, andintraperitoneal administration. Pulmonary delivery may be achieved bynebulization, aerosol inhalation, or dry powder inhalation. Productsdeveloped for administration using these alternate delivery routes willhave compositions recognized by those skilled in the art, as describedin Remington: The Science and Practice of Pharmacy, 19^(th) Edition,Mack Publishing Company, Easton Pa., (1995).

In one variation, the dapsone compositions are administered to protectindividuals against UV-induced skin damage such as sunburn, malignantskin tumors, premalignant lesions, and wrinkles. Typically, the dapsonecompositions are administered once daily, but may be administered morefrequently if desired. In another variation, the dapsone compositionsare administered to prevent premalignant skin lesions from progressingto malignant skin tumors in individuals.

The dapsone compositions are administered to selected individuals. By“selected” it is meant individuals in whom UV protection is considereddesirable because of age, frequent or long duration of exposure to UVradiation, e.g., sun, and/or because they possess an increased risk forUV radiation-induced skin damage. For example, individuals at increasedrisk are those who are more prone to sunburn or develop pigmentedlesions after sun exposure, or who due to genetic makeup, have acondition that predisposes them to skin cancer, e.g., xerodermapigmentosum. Furthermore, individuals with a prior medical history of aUV-induced skin disorder or who present with UV-induced skin damage atthe time the need for UV protection is determined are at increased risk.

The dapsone compositions are typically administered before theindividual engages in an activity that involves UV radiation exposure.The activity may be an outdoor activity such as sunbathing, walking,running, swimming, biking, and the like, engaged in for purposes ofrecreation or physical fitness. The dapsone compositions may also beadministered to individuals engaging in indoor activities, e.g., indoortanning or laboratory work that involves exposure to ultraviolet light.

Method for Preparing the Dapsone Dermatological Composition

In general, the method for producing a dermatological gel compositionhaving dissolved dapsone and microparticulate dapsone precipitatescomprises the steps of completely dissolving dapsone in a solvent orsolvent mixture; adding and adequately dispersing a polymeric thickenerin water; and combining the dissolved dapsone with the dispersedpolymeric thickener. Alternatively, water may be slowly added to thedissolved dapsone, followed by the addition of a polymeric thickener.Ethoxydigylcol and 1-methyl-2-pyrollidone are preferred solvents for usein the topically applied dermatological composition.

In one embodiment, the method for preparing a topically applieddermatological composition having dissolved and microparticulate dapsonecomprises the steps of forming a homogenous dispersion by stirringpurified water vigorously enough to form a vortex and sifting gelpolymer into the vortex formed in the water while continuing to stir;forming a pharmaceutical component by dissolving methyl paraben andpropylparaben in DGME by mixing to form a solution, and mixing dapsonewith the solution until the pharmaceutical is dissolved; mixing thepharmaceutical component with the homogenous dispersion to form amicroparticulate dapsone dispersion; and adding a caustic material.

In another embodiment, the method for preparing a topically applieddermatological composition having only dissolved dapsone includes thesteps of dissolving dapsone in an oil phase or mixed solvent system. Thedissolved dapsone is then combined with the water phase of an emulsionor thickeners or other cosmetic or pharmaceutical excipients to form adermatological product. This topical cream, lotion, solution, ointmentor other topical formulation will contain only dissolved dapsone atambient conditions.

In yet another embodiment, the method for preparing a topically applieddermatological composition having primarily dispersed dapsone includesthe step of dispersing dapsone in a water phase, non-solvating solventor mixed solvent system. The dispersed dapsone is then combined with theoil phase of an emulsion or thickeners or other cosmetic orpharmaceutical excipients to form a dermatological product. This topicalcream, lotion, suspension, ointment or other topical formulation willcontain dispersed dapsone particles and minimal (less than about 5%)dissolved dapsone at ambient conditions.

The order in which reagents are combined may be important, depending onthe particular reagents necessary for the target mixture. For example,after a pharmaceutical such as dapsone is dissolved in a solvent such asDGME, water may be slowly added to the dapsone in the DGME solution, orthe dapsone in DGME solution may be added to the water with mixing.Adding the dapsone in DGME solution to water may result in lesspolydispersity in the size of the microparticulates than adding water tothe dapsone in DGME solutions. The carbomer is generally dispersed inthe water component of the formulation, while the remaining ingredientswill be dissolved or dispersed in whichever of the two components arebest for dissolving or dispersing the ingredient. For example, it issuggested to dissolve methylparaben, propylparaben, and BHA in DGME.After the DGME component and water component are combined, neutralizeris added to formulate the gel.

EXAMPLES

The following example is provided to show that dapsone has an unexpectedprotective benefit in the treatment of ultraviolet radiation-inducedskin tumors.

Those skilled in the art will recognize that while specific embodimentshave been illustrated and described, various modifications and changesmay be made without it departing from the spirit and scope of theinvention.

Example 1 Effect of Dapsone on Skin Tumor Formation in Mice

Example 1 demonstrates the protective effect of dapsone on UV-inducedskin tumor formation. Male and female albino hairless Crl:SKH1-hrBR mice(36/sex/group) were obtained from Charles River Laboratories(Wilmington, Mass.) and individually housed in custom-designed stainlesssteel irradiation cages.

The experimental dapsone formulations (50 μl/mouse, Monday throughFriday) were administered to the dorsum and sides of the mice to an areaof approximately 25 cm² using a glass rod, and the mice irradiated oncedaily, 5 days per week, for 40 weeks. Aqueous carbomer gels containing1% dapsone/10% DGME (diethylene glycol monoethyl ether); 3%dapsone/17.5% DGME; or 5% dapsone/25% DGME were chosen fromrange-finding studies. A vehicle control aqueous carbomer gel contained25% DGME. Formulations were administered one hour before irradiation onMonday, Wednesday, and Friday and one hour after irradiation on Tuesdayand Thursday. Mice were then maintained without being dosed for anadditional 12 weeks for a total of 52 weeks.

The simulated solar radiation (SSR) source was a 6.5 kilowatt zenon longarc water-cooled burner, filtered by a 1 mm thick Schott WG 320 dopedglass filter. During exposure the mice were continuously monitored by acustomized detector, which records both intensity and cumulative UVRdose in Robertson-Berger Units (RBU, 400 RBU approximates one minimalerythema dose (MED) in previously untanned human skin). The low UVRcalibration group (120 RBU/daily, 600 RBU/week) produced an appropriatetumor median latent period for comparison with other groups. The highUVR calibration group (240 RBU/day, 1200 RBU/week) produced asignificant decrease in median tumor latent period. The test level ofUVR (600 RBU per week) permits detection of a modified photocarcinogenicresponse by the test system in response to a test article. Over thecourse of the study, the daily UVR dose was consistent and the totaldose across groups was appropriate.

All mice were observed for viability at least twice daily, and weeklyfor general skin observations. Other clinical observations were recordedweekly; body weights were recorded weekly for the first 13 weeks, andthen every four weeks thereafter and at sacrifice. Individual UV-inducedskin tumor data (size and location) were electronically recorded. Anymouse bearing a tumor>10 mm planar diameter was sacrificed. Furthermore,all mice in a group were sacrificed when:

1) fewer than 50% of the mice per sex survived;2) more than 50% of the surviving mice in the group had tumors of atleast 4 mm (planar diameter); and3) the Study Director reviewed the data and approved the sacrifice.

Tables, graphs, and statistical testing of tumor data were provided asoutput from the ROELEE program (P. N. Lee Statistics and Computing,Ltd., Sutton, United Kingdom). Group comparisons of tumor prevalencewere based on the methods described by Peto and colleagues (Peto, R.,et. al. (1980). Guidelines for Simple, Sensitive Significance Tests forCarcinogenic Effects in Long-Term Animal Experiments. IARC Monographs,Supplement 2. Long-Term and Short-Term Screening Assays for Carcinogens:A Critical Appraisal).

Since bi-directiorial effects on carcinogenicity are plausible, testingwas based on two-tailed probabilities (i.e., the null hypothesis statesthat the superimposed variable does not alter carcinogenicity).Evaluations were based on two-group comparisons. Statisticalinterpretation was based primarily on tumors at least 1 mm in diameterusing the following descriptive parameters:

1) “Median Onset” or “Median Week to Tumor”: The time at which one-halfof the members of other groups have acquired one or more qualifyingtumors, and the associated 95% confidence interval. Separate estimatesevaluated “biased” medians (based on survivors) and mortality-adjustedmedians.2. “Mortality-Free Prevalence”: The proportion of mice in a groupexhibiting one or more qualifying tumors, as a function of time, andadjusted for the effects of competing mortality. This descriptor is thecomplementary probability to the Kaplan-Meier “probability of survivalwithout a tumor” and is derived form calculations of the Kaplan-Meiertype (Kaplan, E. L., and Meier, P. J. Am. Stat. Assoc. 53:457-481(1958)).3. “Tumor Yield”: The number of tumors present, divided by the number ofsurviving mice (i.e., average number of tumors per mouse).4. “Survival”: The absolute number of mice alive at the time ofobservation, compared to the initial number in each group.

Table 1 shows that the Unbiased Median Weeks to Tumor was unaffected bythe vehicle formulation (25% DGME vehicle), and delayed in groupsadministered the dapsone formulations and exposed to 600 RBU/week. Thegroup exposed to high UVR (1200 RBU/week), served as a positive controlto show that the Unbiased Median Weeks to Tumor was accelerated. Theunbiased median latent period was not achieved by the end of the studyfor the 3% dapsone/17.5% DGME gel group, or for the 5% dapsone/25% DGMEgel group for male mice. An entry of 53 weeks is used in Table 1 toillustrate this fact. Dapsone increased the Unbiased Median Weeks toTumor in a dose-dependent manner, indicating a reduction in thephotocarcinogenic response of the mice to UVR in these groups.

FIG. 1 shows the prevalence by week of the first 1 mm tumor for thesexes combined. In comparison with the 25% DGME vehicle formulationadministration (line 1), all dapsone containing gels (line 2, 1% dapsonegel; line 3, 3% dapsone gel; line 4, 5% dapsone gel) significantlyreduced the development of skin tumors in mice exposed to 600 RBU/weekfor the sexes combined (p<0.001 for 1%, 3%, and 5% dapsone gel), in malemice (data not shown, p<0.01 for 1% dapsone gel, and p<0.001 for 3%dapsone gel, and <0.001 for 5% dapsone gel), and in female mice (datanot shown, p<0.01 for 1% and 3% dapsone gel and p<0.001 for 5% dapsonegel). The prevalence of 1 mm tumor formation in untreated mice exposedto 600 RBU/week (line 5) paralleled that of mice administered the 25%DGME vehicle formulation (line 1). Line 6 demonstrates the increase inskin tumor formation in untreated mice exposed to 1200 RBU/week.

The Tumor Potency Ratio (TPR) expresses the influence of a test articleon the skin's response to UVR exposure. The concept of TPR depends onthe relationship between the weekly UVR dose, as a measure of stimulusrate, and the chosen response measure of Unbiased Median Week to Tumorfor each group (tumors >1 mm). With those values and the dose ratecalibration for the untreated 600 RBU/week and 1200 RBU/week groups, theapparent radiation dose rate of the groups was calculated. Thedifference from the nominal rate represents the effect of a testvariable on UVR dose delivery. Since unbiased median latent period wasnot achieved by the end of the study (52 weeks) for the 3% dapsone gelgroup, or the 5% dapsone gel group for males, the estimated TPR wascalculated from the estimated unbiased median latent period of 53 weeks.As shown in Table 2, the TPR was reduced with dapsone application in adose-dependent manner in sexes combined, indicating a dose-dependentinhibitory effect on UVR-induced skin tumor production. The vehicleformulation had no effect on TPR.

Furthermore, biologically important and/or statistically significantreductions occurred in erythema, edema, flaking and/or thickening in thegroups of male and/or female mice administered dapsone formulations(data not shown).

In sum, the administration of the vehicle or dapsone formulations didnot enhance photocarcinogenesis; rather, the dapsone formulationsprotected against UV radiation-induced skin tumor development. Thisconclusion is supported by the tumor endpoints Unbiased Median Weeks toTumor, Peto Analysis of Tumor Onset, Prevalence Curves, Tumor Yield perSurvivor and Tumor Potency Ratio. These observations also suggest areduction in the UV radiation-induced inflammatory process in the groupsadministered the dapsone formulations.

All publications and patent applications cited in this application areherein incorporated by reference in their entirety. Although theforegoing invention has been described by way of illustration andexample for purposes of clarity and understanding, it will be readilyapparent to those of ordinary skill in the art in light of the teachingsof this invention that certain changes and modifications may be madethereto without departing from the spirit or scope of the appendedclaims.

TABLE 1 Unbiased Median Weeks to Tumor for Tumors ≧1 mm 25% 1% Dapsone3% Dapsone 5% Dapsone DGME in a 10% in a 17.5% in a 25% FormulationVehicle DGME Gel DGME Gel DGME Gel None None UVR Exposure RBU/Week 600600 600 600 600 1200 Sexes Combined (weeks) 41.5 47.50 48.00 49.00 41.5024.50 Males (weeks) 45.25 50.00 53.00 53.00 44.00 25.00 Females Median(weeks) 39.50 45.00 45.50 49.00 39.50 24.00

TABLE 2 Tumor Potency Ratios (≧1 mm Tumor Size) 25% 1% Dapsone 3%Dapsone 5% Dapsone DGME in a 10% in a 17.5% in a 25% Formulation VehicleDGME Gel DGME Gel DGME Gel None None UVR Exposure RBU/Week 600 600 600600 600 1200 Sexes Combined 1.00 0.84 0.83 0.80 1 2 Males 1.06 0.97 0.850.80 1 2 Females Median 1.00 0.86 0.82 0.74 1 2

1-29. (canceled)
 30. A method for preventing a premalignant skin lesionfrom becoming a malignant skin tumor comprising administering acomposition to an individual having at least one premalignant skinlesion, wherein said composition comprises dapsone.
 31. A method forpreventing UV-induced malignant skin tumor formation in an individualcomprising: a) selecting the individual in need of protection from UVradiation; and b) administering a composition to the individual, whereinsaid composition comprises dapsone.